This invention relates to the field of telecommunications, and more particularly to frame synchronization and fault protection for a telecommunications device.
Many telecommunications devices include backplanes for transmitting digital information between components of the devices. For example, a telecommunications switching system might include a backplane for transmitting digital data representing voice signals between cards associated with incoming and outgoing ports. Typically, such a system would also include a mechanism to allow the system to detect a framing error or other loss of synchronization between cards, which may occur as a result of a total or partial failure of one of the cards. Successful operation of the system in many instances will depend heavily upon the ability of this mechanism to appropriately detect and respond to such a failure to meet often stringent availability, flexibility, and other requirements placed on the system.
As the telecommunications industry continues to dominate the growth of the global economy, meeting availability, flexibility, and other requirements placed on switching and other systems has become increasingly important. High availability is generally considered as exceeding 99.999 percent availability, amounting to less than approximately five minutes of xe2x80x9cdown timexe2x80x9d per year, and generally requires a system to be able to detect and to autonomously handle certain faults, such as failure of a card causing framing errors or other losses of synchronization, without immediate human intervention. Providing high availability is often a de facto if not explicit competitive requirement for many telecommunications manufacturers.
However, previous techniques for detecting and responding to a framing error or other loss of synchronization are often inadequate to meet high availability and other requirements. One such technique involves comparing, at each card and for each frame, reference signals received from each of two signal generators to detect a framing error or other loss of synchronization between the card and one or both of the generators. If a framing error is detected, the system might raise an alarm to indicate the error, but might otherwise provide no indication of the source of the errorxe2x80x94one generator, both generators, or the card itself Previous techniques also do not allow the system to continue operating, uninterrupted and maintaining the integrity of data the system is handling, despite failure of one of these components, which may result for example in dropped calls and other undesirable consequences. These and other deficiencies of previous techniques become particularly apparent within high availability backplane environments of telecommunications devices.
According to the present invention, disadvantages and problems associated with frame synchronization and fault protection in telecommunications devices have been substantially reduced or eliminated.
According to one embodiment of the present invention, a telecommunications device includes a synchronization bus. A first controller coupled to the bus generates first pulses and communicates the first pulses using the bus. A second controller coupled to the bus generates second pulses synchronized with the first pulses and communicates the second pulses using the bus. A card coupled to the bus receives the first and second pulses and generates internal pulses synchronized with the first and second pulses. The card compares at least one internal pulse with at least one first pulse to detect a loss of synchronization between the internal pulse and the first pulse. The card indicates this loss of synchronization and the second controller may determine a failure of the first controller in response to at least the indication from the card. In a more particular embodiment, the device may be a switching unit having a high availability backplane environment, the first and second pulses may be frame pulses having time slots, and the loss of synchronization may be associated with a framing error.
The present invention provide a number of important technical advantages over previous techniques for detecting and responding to framing errors or other losses of synchronization, in particular within a high availability backplane environment of a telecommunications device. The present invention provides multiple layers of fault protection, including detection, source identification, and handling of faults associated with cards within the device, helping to prevent single points of failure from propagating in the system, reduce down time, and satisfy high availability and other requirements. Unlike previous techniques, the present invention uses internal pulses generated at one or more cards within the system to monitor synchronization between the first controller, the second controller, and the cards. Also unlike previous techniques, rather than merely detecting a framing error or other loss of synchronization, the present invention allows the source of the error to be readily identified and the error handled accordingly, protecting operation of the system from the fault responsible for the error and maintaining the integrity of data the system is handling. As a result of these and other important technical advantages, the present invention is well suited for incorporation in a wide variety of switching and other modern telecommunications devices.